1. Field of the Invention
The present invention relates to a trace control method for use when machining a metal mold or the like, and more specifically, to a trace control method by which some axes are controlled by an NC command.
2. Description of the Related Art
A control method is used for moving two axes by a numerical control (NC) command and controlling the remaining one axis to carry out a tracing. In this method, for example, the X- and Y-axes are controlled by an NC command and a Z-axis is controlled to carry out a tracing operation. More specifically, the X- and Y-axes are controlled by the NC command and the Z-axis is controlled by the following expression. EQU Vz=(.epsilon.-.epsilon..sub.0).times.G
where, Vz is a tracing speed of the Z-axis, .epsilon. is a composite amount of displacement of the X-, Y- and Z-axes, and .epsilon..sub.0 is a standard amount of displacement.
The above trace control method enables any point or path on an X-Y plane to be traced, and thus is very convenient for partially tracing a complex configuration or the like.
Nevertheless, the above method has a low accuracy and the tracing speed cannot be increased because the tracing is carried out for only one axis, and the indexing and distribution are not carried out for the three axes.
In particular, since the indexing and distribution are not carried out, when a tracer head traces an upward plane in the direction in which the tracer head is moving, the head tends to bite into the surface of the model. Conversely, when the tracer head traces a downward plane, the head tends to move away therefrom. As a result, a problem arises in that, when the tracer head is moved forward and then backward, a step is produced at the position at which the upward tracing movement is changed to a downward tracing movement.